Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$48.82	12.364%	$54.8561	$54.86	$54.85	$54.90
Purchase #2	$179.89	5.846%	$190.4064	$190.41	$190.40	$190.40
Purchase #3	$60.99	7.215%	$65.3904	$65.39	$65.40	$65.40
Purchase #4	$119.27	5.186%	$125.4553	$125.46	$125.45	$125.50
Purchase #5	$27.93	11.370%	$31.1056	$31.11	$31.10	$31.10
Purchase #6	$10.58	11.549%	$11.8019	$11.80	$11.80	$11.80
Purchase #7	$50.38	8.663%	$54.7444	$54.74	$54.75	$54.70
7 purchase totals =	$497.86		$533.7601	$533.77	$533.75	$533.80